1. Field of the Invention
The present general inventive concept relates to a developing device and an image forming apparatus having the same, and, more particularly, to an image forming apparatus having a developing member to supply a developer to a photosensitive member on which an electrostatic latent image is formed.
2. Description of the Related Art
Generally, a developing device and an image forming apparatus having the same are used to form an image on a recording medium such as paper according to an input image signal.
Conventional image forming apparatuses principally include a body defining an external appearance of the apparatus, a paper supply unit to supply a recording medium such as paper, a developing device to develop an image on the recording medium, a fixing unit to fix the image on the recording medium by applying heat and pressure to the recording medium, etc. The developing device includes an exposure unit to irradiate a laser beam containing image information, a photosensitive member having a surface on which an electrostatic latent image is formed by the exposure unit, and a developing member to supply a developer to the photosensitive member so as to form a visible image on the photosensitive member.
Referring to FIG. 1 illustrating one exemplary conventional image forming apparatus, a developing member 2 is spaced apart from an outer circumferential surface of a photosensitive member 1 such that a developer is transmitted to the photosensitive member 1 in a non-contact manner by an electrostatic field between the photosensitive member 1 and the developing member 2. To enable the transmission of developer from the developing member 2 to the photosensitive member 1 by the electrostatic field, power is applied to both the photosensitive member 1 and the developing member 2 of the conventional image forming apparatus.
Using the above-described conventional image forming apparatus, since a relatively large amount of developer is used when developing a dark solid image, whereas a relatively small amount of developer is used when developing a light halftone image, development of the solid image applies a higher voltage to the photosensitive member 1 than development of the halftone image and consequently, causes a greater electrostatic force to be generated from the photosensitive member 1 than development of the halftone image. Accordingly, when developing the solid image, a developer is adsorbed from the developing member 2 to the photosensitive member 1 at a position farther away from the photosensitive member 1. Also, when developing the halftone image, as illustrated in FIG. 2, a developer is adsorbed from the developing member 2 to the photosensitive member 1 at a position closer to the photosensitive member 1.
In the above-described conventional image forming apparatus, however, since the developer is adsorbed to the photosensitive member at a position farther away from the photosensitive member upon development of the solid image than development of the halftone image, there is a problem in that, when a desired to develop the solid image and the halftone image in sequence exists, a portion of the developer for use in formation of the halftone image is prematurely adsorbed to the photosensitive member, thereby being used to develop the solid image rather than being used to form the halftone image, and causing defects in the resulting halftone image.
Furthermore, after extended use of the image forming apparatus, a surface of the developing member is liable to accumulate fine scratches due to frictional force applied thereto. Such a scratched surface region cannot properly retain the developer, making adsorption of the developer to a corresponding region of the photosensitive member difficult to ensure, and resulting in image defects.